Adaptive clock signal frequency scaling

ABSTRACT

Systems, methods, and circuitries are disclosed generating a dynamic clock signal having a dynamic clock signal frequency for a data processing system from an input clock signal having an input clock signal frequency. In one example, adaptive frequency scaling circuitry includes scaling control circuitry and clock gating circuitry. The scaling control circuitry includes hardware configured to receive a performance indicator value indicative of an operating parameter of the data processing system and select a dynamic clock gating control value based at least on the performance indicator value. The clock gating circuitry is configured to receive the dynamic clock gating control value, and in response, selectively gate the input clock signal based on the dynamic clock gating control value to generate the dynamic clock signal.

BACKGROUND

Power optimization has become an important goal in integrated circuitdesign as integrated circuits are called upon to provide increasingfunctionality as the electronic devices that include the integratedcircuits shrink in physical size. Clock tree power consumes up to 70% oftotal integrated circuit power and modern integrated circuit designs at40 nm and below experience significantly increased clock tree powerconsumption. Power consumption is directly proportional to the voltageand frequency of the clock tree.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary adaptive frequency scaling circuitrygenerating a dynamic clock signal from an input clock signal for a dataprocessing system in accordance with various aspects described.

FIG. 2 illustrates an exemplary adaptive frequency scaling circuitrygenerating a dynamic clock signal and a fixed clock signal from an inputclock signal for a data processing system in accordance with variousaspects described.

FIG. 3 illustrates an exemplary clock gating circuitry for use ingenerating the dynamic clock signal in accordance with various aspectsdescribed.

FIG. 4 illustrates an exemplary scaling circuitry for use in generatingthe dynamic clock signal in accordance with various aspects described.

FIG. 5 illustrates an exemplary flow diagram of an exemplary method ofadaptively scaling an input clock signal frequency in accordance withvarious aspects described.

DESCRIPTION

Because power consumption is directly related to clock signal frequency,many devices include means for reducing clock signal frequency whenoperating conditions of the device allow for satisfactory deviceperformance at the reduced clock signal frequency. In many existingsolutions, software is used to adjust the clock signal frequencyaccording to the activity level of hardware components in the device.However, software-based control of clock signal frequency has a slowresponse time and may result in a drop in performance (e.g., packet lossin a networking device) in fast changing scenarios. Another disadvantageis that these solutions often rely on multiple phase locked loops (PLLs)to generate clock signals with different frequencies or divider circuitsthat can generate clocks signals with frequencies that are an integerfractions (e.g., ½, ⅓, . . . , and so on) of the original clock signalfrequency.

Described herein are systems, circuitries, and methods that adaptivelyand dynamically generate a clock signal having a dynamic clock signalfrequency that is determined based on operating conditions. Thedescribed adaptive clock signal generation systems, circuitries, andmethods are hardware based rather than software based, meaning that theresponse time can be immediate (i.e., a single input clock signalcycle). Further, only a single PLL is needed and clock signalfrequencies can be generated with a much finer granularity as comparedto simple divider-based solutions.

The present disclosure will now be described with reference to theattached figures, wherein like reference numerals are used to refer tolike elements throughout, and wherein the illustrated structures anddevices are not necessarily drawn to scale. As utilized herein, terms“module”, “component,” “system,” “circuit,” “element,” “slice,”“circuitry,” and the like are intended to refer to a set of one or moreelectronic components, a computer-related entity, hardware, software(e.g., in execution), and/or firmware. For example, circuitry or asimilar term can be a processor, a process running on a processor, acontroller, an object, an executable program, a storage device, and/or acomputer with a processing device. By way of illustration, anapplication running on a server and the server can also be circuitry.One or more circuits can reside within the same circuitry, and circuitrycan be localized on one computer and/or distributed between two or morecomputers. A set of elements or a set of other circuits can be describedherein, in which the term “set” can be interpreted as “one or more.”

As another example, circuitry or similar term can be an apparatus withspecific functionality provided by mechanical parts operated by electricor electronic circuitry, in which the electric or electronic circuitrycan be operated by a software application or a firmware applicationexecuted by one or more processors. The one or more processors can beinternal or external to the apparatus and can execute at least a part ofthe software or firmware application. As yet another example, circuitrycan be an apparatus that provides specific functionality throughelectronic components without mechanical parts; the electroniccomponents can include one or more processors therein to executeexecutable instructions stored in computer readable storage mediumand/or firmware that confer(s), at least in part, the functionality ofthe electronic components.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be physicallyconnected or coupled to the other element such that current and/orelectromagnetic radiation (e.g., a signal) can flow along a conductivepath formed by the elements. Intervening conductive, inductive, orcapacitive elements may be present between the element and the otherelement when the elements are described as being coupled or connected toone another. Further, when coupled or connected to one another, oneelement may be capable of inducing a voltage or current flow orpropagation of an electro-magnetic wave in the other element withoutphysical contact or intervening components. Further, when a voltage,current, or signal is referred to as being “applied” to an element, thevoltage, current, or signal may be conducted to the element by way of aphysical connection or by way of capacitive, electro-magnetic, orinductive coupling that does not involve a physical connection.

As used herein, a signal that is “indicative of” a value or otherinformation may be a digital or analog signal that encodes or otherwisecommunicates the value or other information in a manner that can bedecoded by and/or cause a responsive action in a component receiving thesignal. The signal may be stored or buffered in computer readablestorage medium prior to its receipt by the receiving component and thereceiving component may retrieve the signal from the storage medium.Further, a “value” that is “indicative of” some quantity, state, orparameter may be physically embodied as a digital signal, an analogsignal, or stored bits that encode or otherwise communicate the value.

Use of the word example is intended to present concepts in a concretefashion. The terminology used herein is for the purpose of describingparticular examples only and is not intended to be limiting of examples.As used herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elementsand/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components and/or groups thereof.

In the following description, a plurality of details is set forth toprovide a more thorough explanation of the embodiments of the presentdisclosure. However, it will be apparent to one skilled in the art thatembodiments of the present disclosure may be practiced without thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form rather than in detail in order to avoidobscuring embodiments of the present disclosure. In addition, featuresof the different embodiments described hereinafter may be combined witheach other, unless specifically noted otherwise.

FIG. 1 illustrates a data processing system 100 that receives a dynamicclock signal having a frequency F_(out_dyn) from an exemplary adaptivefrequency scaling circuitry 110. The data processing system 100 includesdigital electronic components such as integrated circuits (not shown)that input and operate according to the dynamic clock signal. In some ofthe examples below, the data processing system 105 is a networkprocessing system. However, the data processing system can be any systemthat includes components clocked by the dynamic clock signal and thatreceives ingress data, manipulates the data, and produces egress data.

The adaptive frequency scaling circuitry 110 generates the dynamic clocksignal from an input clock signal having a frequency F_(in). Theadaptive frequency scaling circuitry 110 includes scaling controlcircuitry 120 and clock gating circuitry 130. The scaling controlcircuitry 120 includes hardware configured to receive a performanceindicator value indicative of an operating parameter of the dataprocessing system. The operating parameter is some characteristic of thedata processing system (e.g., number of active links, buffer usage, andso on) that can be used to determine an appropriate clock signalfrequency. The scaling control circuitry 120 hardware selects a dynamicclock gating control value N_(dyn) based at least on the performanceindicator value, where N is an integer. The clock gating circuitry 130receives the dynamic clock gating control value and, in response,selectively gates the input clock signal based on the dynamic clockgating control value to generate the dynamic clock signal.

FIG. 2 illustrates an exemplary adaptive frequency scaling circuitry 210that generates a dynamic clock signal and a fixed clock signal for anetwork processing system 200. The network processing system 200includes an ingress data interface that receives packets from externalcomponents and an egress interface that transmits packets to externalcomponents. A store direct memory access (DMA) receives packets from theingress data interface and stores the packets to shared packet buffer.The shared packet buffer stores and queues the packets to be processedand to be fetched. A packet processing unit reads full or partialpackets and classifies the packets. The packet processing unit may alsomodify packets in the shared packet buffer. A fetch DMA fetches thepackets from the shared packet buffer and transmits the packets to anegress data interface.

The various functional components of the network processing system 100are implemented with several ICs (shown as the boxes). The distributionof the functional components of the network processing system amongstICs may be different that that shown in FIG. 2 in other examples (i.e.,some functional components may be provided on the same IC while otherfunctional components are distributed amongst several ICs). Someelectronic components in a given IC may require a fixed clock frequencywhile other components may be capable of operating at different clockfrequencies. Because of this, the adaptive frequency scaling circuitry210 generates a dynamic clock signal having a dynamic clock frequencythat changes according to the performance indicator value and a fixedclock signal that has a constant clock frequency regardless of theperformance indicator value. For the purposes of this description, thedynamic clock signal has a dynamic clock frequency that is changed byadaptive frequency scaling circuitry according to operating conditionsof the data processing system, while the fixed clock signal has a fixedclock frequency that remain constant to provide an unchanging clocksignal for IC components that require a constant clock. The scalingcontrol circuitry 220 generates a dynamic clock gating control valueN_(dyn) based on the performance indicator value. The scaling controlcircuitry 220 generates a fixed clock gating signal N_(fix) that willresult in the frequency of the fixed clock signal remaining the sameregardless of the performance indicator value.

The adaptive frequency scaling circuitry 210 includes a dynamic clockgating circuitry 230 a that generates the dynamic clock signal and afixed clock gating circuitry 230 b that generates the fixed clocksignal. As will be described in more detail with reference to FIG. 3,the dynamic clock gating circuitry 230 a selectively gates the inputclock signal based on the dynamic clock gating control value to generatethe dynamic clock signal. The fixed clock gating circuitry 230 bselectively gates the dynamic clock signal based on the fixed clockgating control value to generate the fixed clock signal. The fixed clockgating circuitry 230 b gates the dynamic clock signal, rather than theinput clock signal, so that the dynamic clock signal and fixed clocksignal remain in synchronization. Both clock signals are provided by wayof a clock tree 215 to the ICs in the network processing system.

The scaling control circuitry 220 determines the clock gating controlvalue for each clock gating circuitry based on performance indicatorsthat include the link rate of the ingress interface and the egressinterface, the link activity of the ingress interface and the egressinterface, and one or several queue lengths in the shared packet buffer.Of course, in other examples different or additional performanceindicators are used. As will be described in more detail with referenceto FIG. 4, the scaling control circuitry 220 includes pre-configuredlookup tables that each map dynamic clock gating control values andfixed clock gating control values to values for one of the performanceindicators.

In some examples, the scaling control circuitry 220 includes triggercircuitry 223 that causes the scaling control circuitry to generate newclock gating control values based on the current value of theperformance indicator. For example, the trigger circuitry 223 may beconfigured to count a predetermined integer number x of input clockcycles and cause the scaling control circuitry 220 to generate new clockgating control values on every xth input clock cycle. In other examples,the trigger circuitry 223 be configured to detect a change in theperformance indicator value and cause the scaling circuitry to generatenew clock gating control values when a performance indicator valuechange of a given significance occurs. In another example, the hardwareof the scaling control circuitry 220 is clocked by the input clocksignal and the clock gating control values are generated every cycle ofthe input clock signal.

FIG. 3 illustrates an exemplary M bit clock gating circuitry 330 thatscales an original clock frequency F_(orig) (which can be either theinput clock frequency F_(in) or the dynamic clock frequency F_(out_dyn))to a desired clock frequency F_(des). Over every 2^(M) original clocksignal cycles, the clock gating circuitry passes N original clock signalpulses of the original clock signal to generate a desired (e.g., dynamicor fixed) clock signal having the desired clock frequency.

The clock gating circuitry 330 includes accumulator circuitry 332,register circuitry 334, and gate circuitry 336. The accumulatorcircuitry 332 has M+1 bits with the most significant bit (MSB) M beingan overflow bit. On every original clock signal cycle, the accumulatorcircuitry 332 receives M+1 bits corresponding to the value of N by wayof a first input and M bits from the register circuitry 334 by way of asecond input. The register circuitry 334 stores the values of the M−1:0bits of the accumulator circuitry 332 in the prior clock cycle. Thus,with every cycle of the original clock signal, the content ofaccumulator circuitry 332 is increased by N. The gate circuitry 336includes latch circuitry 336 a and AND circuitry 336 b. The latchcircuitry 336 a stores a value of 1 for every 0 value in the originalclock signal. The MSB (bit M) of the accumulator is the clock enable ofthe latch circuitry 336 a that causes the latch circuitry 336 a tooutput the stored 1 value. The AND circuitry 336 b outputs an originalclock signal pulse when the output value of the latch circuitry 336 a is1 to generate the desired clock signal.

The desired clock signal has a desired clock frequency F_(des)corresponding to F_(orig)·N/2^(M). With M being fixed by the size of theaccumulator, the clock gating control value that will produce a desiredclock frequency from a known original clock frequency can be determinedas F_(des)·2^(M)/F_(orig). For example given an 8 bit accumulatorcircuitry 332, when F_(des)=F_(orig) then N is 256 (2⁸). This means thatwith every cycle of the original clock, the accumulator circuitry adds0x100 (N) to 0x00 (contents of register circuitry 334) and the output ofthe accumulator is 0x100. Since the MSB of the accumulator content is 1on every original clock cycle, the gate circuitry will pass every pulseof the original clock signal. With the same 8 bit accumulator circuitry332, when F_(des)=½ F_(orig) then N is 128 (0x80). This means that withevery even cycle of the original clock, the accumulator circuitry adds0x80 (N) to 0x00 (contents of register circuitry 334) and the output ofthe accumulator is 0x80 meaning that the gate circuitry 334 does notpass an original clock signal pulse. With odd even cycle of the originalclock, the accumulator circuitry adds 0x80 (N) to 0x80 (contents ofregister circuitry 334) and the output of the accumulator is 0x100meaning that the gate circuitry 334 does pass an original clock signalpulse. Since the MSB is 1 on every other original clock signal cycle,the gate circuitry 334 will pass every other pulse of the original clocksignal.

With the illustrated clock gating circuitry 330, the desired frequencygranularity is very fine. For example, with M=7, +/−1% adjustment of theoriginal clock frequency can be achieved. Also, the clock pulses in thedesired clock signal are evenly enabled such that, for example, when M=7and N=96, 75% of the clock frequency can be achieved.

FIG. 4 illustrates an exemplary scaling control circuitry 420 thatgenerates the dynamic clock gating control value N_(dyn) and the fixedclock gating control circuitry N_(fix). The scaling control circuitryincludes an interface rate analysis circuitry 421 that receivesperformance indicator values corresponding to an interface rate from theingress data interface (IDI) and the egress data interface (EDI) (seeFIG. 2). The interface rate analysis circuitry 421 finds the highestinterface rate (Highest_Rate) from all the active links between thenetwork processing system and external devices. For example, theinterface rate for each link may be the link speed obtained via an autonegotiation process or an auto polling process. The activity status ofeach link may be indicated by RX_DV (Receive Data Valid) signals from aGMII/MII ingress data interface, RXC (Receive Control) signals from anXGMI ingress data interface, TX_EN (Transmit Enable) signals from aGMII/MII egress data interface, and/or TXC (Transmit Control) signalsfrom an XGMII egress data interface which are analyzed by the interfacerate analysis circuitry 421 to identify the highest interface rate.

The scaling control circuitry 420 includes a highest interface ratelookup table 425 a that maps a dynamic clock gating control valueN_(dyn)′ and a fixed clock gating control value N_(fix)′ to ranges ofvalues for the highest interface rate determined by the interface rateanalysis circuitry 421. In the lookup table 425 a, there are multipleentries. The highest interface rate is compared with the rate rangedefined in each entry, once match is found, then the dynamic clockgating control value N_(dyn)′ and the fixed clock gating control valueN_(fix)′ for the match entry are selected.

The interface rate analysis circuitry 421 also tabulates the totalinterface rate (Total_Rate) from all the active links. For example, theinterface rate for each link may be the link speed obtained via an autonegotiation process or an auto polling process. The activity status ofeach link may be indicated by RX_DV (Receive Data Valid) signals from aGMII/MII ingress data interface, RXC (Receive Control) signals from anXGMI ingress data interface, TX_EN (Transmit Enable) signals from aGMII/MII egress data interface, and/or TXC (Transmit Control) signalsfrom an XGMII egress data interface which are combined by the interfacerate analysis circuitry to calculate the total interface rate. Thescaling control circuitry 420 includes a total interface rate lookuptable 425 b that maps a dynamic clock gating control value N_(dyn)″ anda fixed clock gating control value N_(fix)″ to ranges of values for thetotal interface rate determined by the interface rate analysis circuitry421. In the lookup table 425 b, there are multiple entries. The totalinterface rate is compared with the range defined in each entry, oncematch is found, then the dynamic clock gating control value N_(dyn)″ andthe fixed clock gating control value N_(fix)″ for the match entry areselected.

The scaling control circuitry 420 includes a queue length lookup table425 c that maps a dynamic clock gating control value N_(dyn)′″ and afixed clock gating control value N_(fix)′″ to ranges of values a queuelength for one or more queues in the shared packet buffer (see FIG. 2).In the lookup table 425 c, there are multiple entries. The queue lengthis compared with the range defined in each entry, once match is found,then the dynamic clock gating control value N_(dyn)′″ and the fixedclock gating control value N_(fix)′″ for the match entry are selected.While only a single queue length is illustrated as a performanceindicator in FIG. 4, in some examples, the lengths of multiple queues inthe shared packet buffer may each be a performance indicator, thelengths of multiple queues may be combined as a single performanceindicator, and/or a length of the longest queue may be a performanceindicator.

The scaling control circuitry 420 includes selection circuitry 427 thatfinds the maximum value of the clock gating control values output by thelookup tables 425 a-425 c and the minimum value of the fixed clockgating control values output by the lookup tables 425 a-425 c. Theminimum fixed clock gating control value and the maximum dynamic clockgating control value are selected because the fixed clock frequency doesnot change but the fixed clock signal is derived from the dynamic clocksignal which does change. In this manner the product of N_(dyn) andN_(fix) remains the same and the fixed clock signal will have a constantfrequency. The selection circuitry 427 outputs the selected dynamicclock gating control value N_(dyn) and fixed clock gating control valueN_(fix) to the dynamic clock gating circuitry and the fixed clock gatingcircuitry (see FIG. 2), respectively.

FIG. 5 illustrates a flow diagram outlining an exemplary method 500 forgenerating a dynamic clock gating control value N_(dyn) and fixed clockgating control value N_(fix) for clock gating circuitries based onperformance indicators. The method 500 may be performed by the scalingcontrol circuitry 220 and/or 420 of FIGS. 2 and 4, respectively. Themethod includes, at 505 initializing a value for Highest_Rate,Total_Rate, and a link identifier [i] to 0. Values for Highest_Rate,Total_Rate, and [i] may be stored in registers. At 510 a determinationis made as to whether a next interface [i] is active. If the interface[i] is not active, the method continues to 530 where a check is made asto whether there are any interfaces that have not been analyzed. If at510 the next interface [i] is active, at 515 the Total_Rate value isincrease by the link rate of the interface [i]. At 520 a determinationis made as to whether the link rate of interface [i] is higher than thevalue for Highest_Rate, and if so, at 525 the value for Highest_Rate isreplaced with the link rate of interface [i]. At 530 if the lastinterface has not been analyzed, the method moves to 535 where a nextinterface [i+1] is identified and 510-530 are performed again.

Once all active interfaces have been analyzed, at 540 N_(dyn)′ andN_(fix)′ are selected based on the value for Highest_Rate. At 550N_(dyn)″ and N_(fix)″ are selected based on the value for Total_Rate. At550 N_(dyn)′″ and N_(fix)′″ are selected based on a value for queuelength in a shared packet buffer. At 555, the method includes selectinga maximum of N_(dyn)′, N_(dyn)″, and N_(dyn)″ as dynamic clock gatingcontrol value N_(dyn) and a minimum of N_(fix)′, N_(fix)″, and N_(fix)′″as fixed clock gating control value N_(fix).

While the invention has been illustrated and described with respect toone or more implementations, alterations and/or modifications may bemade to the illustrated examples without departing from the spirit andscope of the appended claims. In particular regard to the variousfunctions performed by the above described components or structures(assemblies, devices, circuits, systems, etc.), the terms (including areference to a “means”) used to describe such components are intended tocorrespond, unless otherwise indicated, to any component or structurewhich performs the specified function of the described component (e.g.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary implementations of the invention.

Examples can include subject matter such as a method, means forperforming acts or blocks of the method, at least one machine-readablemedium including instructions that, when performed by a machine causethe machine to perform acts of the method or of an apparatus or systemfor dynamically generating a clock signal for a data processing systemaccording to embodiments and examples described herein.

Example 1 is an adaptive frequency scaling circuitry configured togenerate a dynamic clock signal having a dynamic clock signal frequencyfor a data processing system from an input clock signal having an inputclock signal frequency. The adaptive frequency scaling circuitryincludes scaling control circuitry and clock gating circuitry. Thescaling control circuitry including hardware is configured to receive aperformance indicator value indicative of an operating parameter of thedata processing system and select a dynamic clock gating control valuebased at least on the performance indicator value. The clock gatingcircuitry is configured to receive the dynamic clock gating controlvalue, and in response, selectively gate the input clock signal based onthe dynamic clock gating control value to generate the dynamic clocksignal.

Example 2 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling control circuitryincludes interface rate analysis circuitry and lookup table. Theinterface rate analysis circuitry is configured to receive signalsindicative of interface rates of active links between the dataprocessing system and external devices; identify a highest interfacerate; and output the performance indicator value indicative of thehighest interface rate. The lookup table is configured to input theperformance indicator value and output a dynamic clock gating controlvalue mapped to the highest interface rate.

Example 3 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling control circuitryincludes interface rate analysis circuitry and a lookup table. Theinterface rate analysis circuitry is configured to receive signalsindicative of interface rates of active links between the dataprocessing system and external devices; compute a total interface ratebased on the interface rates; and output the performance indicator valueindicative of the total interface rate. The lookup table is configuredto input the performance indicator value and output a dynamic clockgating control value mapped to the total interface rate.

Example 4 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling circuitry furtherincludes a lookup table configured to input a performance indicatorvalue indicative of a length of a queue in a shared packet buffer of thedata processing system and output a dynamic clock gating control valuemapped to the queue length.

Example 5 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling circuitry includes aplurality of lookup tables and selection circuitry. The plurality oflookup tables input a respective plurality of performance indicatorvalues and output a respective plurality of dynamic clock gating controlvalues. The selection circuitry is configured to select one of theplurality of dynamic clock gating control values and provide theselected dynamic clock gating control value to the clock gatingcircuitry.

Example 6 includes the subject matter of example 1, including oromitting optional elements, wherein the dynamic clock gating controlvalue is indicative of an integer N and the clock gating circuitryincludes: accumulator circuitry having M+1 bits, wherein the accumulatoris configured to combine a first input value and a second input valueand output M+1 bits corresponding to a sum of the first value and thesecond value, further wherein the first input value is N; registercircuitry configured to store bits M−1 to 0 of the output M+1 bits fromthe accumulator and provide the stored bits to the accumulator as thesecond value; and gate circuitry configured to output the dynamic clocksignal by passing an input clock signal pulse in response to bit M inthe output M+1 bits from the accumulator being 1; and the scalingcontrol circuitry is configured to determine N based at least on adesired frequency and M.

Example 7 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling control circuitrygenerates the dynamic clock gating signal and a fixed clock gatingsignal, the clock gating circuitry includes a first clock gatingcircuitry configured to receive the dynamic clock gating control value,and in response, selectively gate the input clock signal based on thedynamic clock gating control value to generate a dynamic clock signalhaving a desired dynamic clock frequency. A second clock gatingcircuitry is configured to receive the fixed clock gating control value,and in response, selectively gate the dynamic clock signal based on thefixed clock gating control value to generate a fixed clock signal havinga fixed clock frequency, wherein the fixed clock signal frequencyremains constant regardless of the performance indicator value.

Example 8 includes the subject matter of example 7, including oromitting optional elements, wherein the scaling circuitry includes aplurality of lookup tables and selection circuitry. The plurality oflookup tables input a respective plurality of performance indicatorvalues and output a respective plurality of dynamic clock gating controlvalues and a respective plurality of fixed clock gating control values.The selection circuitry configured to select one of the plurality ofdynamic clock gating control values; select one of the plurality offixed clock gating control values, such that the selected fixed clockgating control value, when used to gate the dynamic clock signal, willgenerate a fixed clock signal having the fixed clock signal frequency;and provide the selected dynamic clock gating control value and theselected fixed clock gating control value to the clock gating circuitry.

Example 9 includes the subject matter of example 1, including oromitting optional elements, wherein the scaling control circuitryfurther includes trigger circuitry configured to cause the scalingcontrol circuitry to determine a subsequent desired dynamic clockfrequency for the data processing system on every xth cycle of the inputclock signal, where x is a predetermined integer.

Example 10 is a method, including receiving a performance indicatorvalue indicative of an operating parameter of a data processing system;selecting a dynamic clock gating control value based at least on theperformance indicator value; and gating an input clock signal based atleast on the dynamic clock gating control value to generate a dynamicclock signal.

Example 11 includes the subject matter of example 10, including oromitting optional elements, wherein selecting a dynamic clock gatingcontrol value includes inputting the performance indicator value to alookup table and selecting an output of the lookup table as the clockgating control value.

Example 12 includes the subject matter of example 10, including oromitting optional elements, further including: selecting a fixed clockgating control value based on the dynamic clock gating control value anda fixed clock frequency; and gating the dynamic clock signal based atleast on the fixed clock gating control value to generate a fixed clocksignal having the fixed clock frequency.

Example 13 includes the subject matter of example 10, including oromitting optional elements, wherein gating the input clock signal togenerate the dynamic clock signal includes, for each cycle of the inputclock signal: inputting M+1 bits corresponding to the dynamic clockgating control value to an accumulator having M+1 bits; inputting M bitscorresponding to bits M−1:0 of the accumulator at a prior input clockcycle to the accumulator; and passing an input clock signal pulse inresponse to bit M of the accumulator being 1.

Example 14 includes the subject matter of example 13, including oromitting optional elements, further including determining the dynamicclock gating control value as a product of a desired dynamic clocksignal frequency and 2^(M) divided by an input clock frequency of theinput clock signal.

Example 15 includes the subject matter of example 10, including oromitting optional elements, further including: receiving a performanceindicator value indicative of a plurality of operating parameters of adata processing system; determining a plurality of dynamic clock gatingcontrol values, wherein each of the determined dynamic clock gatingcontrol values in the plurality of dynamic clock gating control valuesis based a different one of the plurality performance indicator values;selecting a maximum dynamic clock gating control value from amongst thedetermined dynamic clock gating control values; and gating an inputclock signal based at least on the maximum dynamic clock gating controlvalue to generate the dynamic clock signal.

Example 16 includes the subject matter of example 10, including oromitting optional elements, wherein the performance indicator value isindicative of one or more of a highest interface rate amongst activelinks between the data processing system and external devices, a highestinterface rate amongst active links between the data processing systemand the external devices, and a queue length in a shared packet bufferin the data processing system.

Example 17 is a clock gating circuitry configured to gate an originalclock signal having an original clock frequency to generate a desiredclock signal having a desired clock frequency based on a clock gatingcontrol value N. The clock gating circuitry includes accumulatorcircuitry having M+1 bits, wherein the accumulator is configured tocombine a first input value and a second input value and output M+1 bitscorresponding to a sum of the first value and the second value, furtherwherein the first input value is N; register circuitry configured tostore bits M−1 to 0 of the output M+1 bits from the accumulator andprovide the stored bits to the accumulator as the second value; and gatecircuitry configured to output the desired clock signal by passing anoriginal clock signal pulse in response to bit M in the output M+1 bitsfrom the accumulator being 1.

Example 18 includes the subject matter of example 17, including oromitting optional elements, wherein the original clock signal is a clocksignal that is output by another clock gating circuitry.

Example 19 is a method, including, until all active interfaces have beenanalyzed: identifying an active interface between a data processingsystem and an external device; increasing a total rate value by a linkrate of the active interface; and replacing a highest rate value withthe link rate when the link rate is higher than the highest rate value;selecting a first dynamic clock gating control value based on the totalrate value; selecting a second dynamic clock gating control value basedon the highest rate value; selecting a third dynamic clock gatingcontrol value based on a queue length value; and providing, to a clockgating circuitry, a maximum of the first dynamic clock gating controlvalue, the second dynamic clock gating control value, and the thirddynamic clock gating control value as a dynamic clock gating controlvalue, wherein the clock gating circuitry generates a dynamic clocksignal from an input clock signal based at least on the maximum dynamicclock gating control value.

Example 20 includes the subject matter of example 19, including oromitting optional elements, further including: selecting a first fixedclock gating control value based on the total rate value; selecting asecond fixed clock gating control value based on the highest rate value;selecting a third fixed clock gating control value based on a queuelength value; and providing, to a second clock gating circuitry, aminimum of the first fixed clock gating control value, the second fixedclock gating control value, and the third fixed clock gating controlvalue as a fixed clock gating control value, wherein a second clockgating circuitry generates a fixed clock signal from the dynamic clocksignal based at least on the minimum fixed clock gating control value.

Various illustrative logics, logical blocks, modules, and circuitsdescribed in connection with aspects disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform functions described herein. Ageneral-purpose processor can be a microprocessor, but, in thealternative, processor can be any conventional processor, controller,microcontroller, or state machine. The various illustrative logics,logical blocks, modules, and circuits described in connection withaspects disclosed herein can be implemented or performed with a generalpurpose processor executing instructions stored in computer readablemedium.

The above description of illustrated embodiments of the subjectdisclosure, including what is described in the Abstract, is not intendedto be exhaustive or to limit the disclosed embodiments to the preciseforms disclosed. While specific embodiments and examples are describedherein for illustrative purposes, various modifications are possiblethat are considered within the scope of such embodiments and examples,as those skilled in the relevant art can recognize.

In this regard, while the disclosed subject matter has been described inconnection with various embodiments and corresponding Figures, whereapplicable, it is to be understood that other similar embodiments can beused or modifications and additions can be made to the describedembodiments for performing the same, similar, alternative, or substitutefunction of the disclosed subject matter without deviating therefrom.Therefore, the disclosed subject matter should not be limited to anysingle embodiment described herein, but rather should be construed inbreadth and scope in accordance with the appended claims below.

In particular regard to the various functions performed by the abovedescribed components (assemblies, devices, circuits, systems, etc.), theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component or structure which performs the specified function of thedescribed component (e.g., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. The use of the phrase “one or more of A, B, orC” is intended to include all combinations of A, B, and C, for exampleA, A and B, A and B and C, B, and so on.

What is claimed is:
 1. Adaptive frequency scaling circuitry configuredto generate a dynamic clock signal having a dynamic clock signalfrequency for a data processing system from an input clock signal havingan input clock signal frequency, the adaptive frequency scalingcircuitry comprising: scaling control circuitry comprising hardwareconfigured to: receive a performance indicator value indicative of anoperating parameter of the data processing system; and select a dynamicclock gating control value based at least on the performance indicatorvalue, wherein the scaling control circuitry comprises a lookup tableconfigured to input the performance indicator value and output a dynamicclock gating control value mapped to the highest interface rate; clockgating circuitry configured to: receive the dynamic clock gating controlvalue; and in response, selectively gate the input clock signal based onthe dynamic clock gating control value to generate the dynamic clocksignal.
 2. The adaptive frequency scaling circuitry of claim 1, whereinthe scaling control circuitry comprises: interface rate analysiscircuitry configured to: receive signals indicative of interface ratesof active links between the data processing system and external devices;identify a highest interface rate; and output the performance indicatorvalue indicative of the highest interface rate.
 3. The adaptivefrequency scaling circuitry of claim 1, wherein the scaling controlcircuitry comprises: interface rate analysis circuitry configured to:receive signals indicative of interface rates of active links betweenthe data processing system and external devices; compute a totalinterface rate based on the interface rates; and output the performanceindicator value indicative of the total interface rate; and a lookuptable configured to input the performance indicator value and output adynamic clock gating control value mapped to the total interface rate.4. The adaptive frequency scaling circuitry of claim 1, wherein thescaling circuitry further comprises a lookup table configured to input aperformance indicator value indicative of a length of a queue in ashared packet buffer of the data processing system and output a dynamicclock gating control value mapped to the queue length.
 5. The adaptivefrequency scaling circuitry of claim 1, wherein the scaling circuitrycomprises: a plurality of lookup tables that input a respectiveplurality of performance indicator values and output a respectiveplurality of dynamic clock gating control values; and selectioncircuitry configured to: select one of the plurality of dynamic clockgating control values; and provide the selected dynamic clock gatingcontrol value to the clock gating circuitry.
 6. The adaptive frequencyscaling circuitry of claim 1, wherein: the dynamic clock gating controlvalue is indicative of an integer N: the clock gating circuitrycomprises: accumulator circuitry having M+1 bits, wherein theaccumulator is configured to combine a first input value and a secondinput value and output M+1 bits corresponding to a sum of the firstvalue and the second value, further wherein the first input value is N;register circuitry configured to store bits M−1 to 0 of the output M+1bits from the accumulator and provide the stored bits to the accumulatoras the second value; and gate circuitry configured to output the dynamicclock signal by passing an input clock signal pulse in response to bit Min the output M+1 bits from the accumulator being 1; and the scalingcontrol circuitry is configured to determine N based at least on adesired frequency and M.
 7. The adaptive frequency scaling circuitry ofclaim 1, wherein: the scaling control circuitry generates the dynamicclock gating signal and a fixed clock gating signal; the clock gatingcircuitry comprises: a first clock gating circuitry configured to:receive the dynamic clock gating control value; and in response,selectively gate the input clock signal based on the dynamic clockgating control value to generate a dynamic clock signal having a desireddynamic clock frequency; and a second clock gating circuitry configuredto: receive the fixed clock gating control value; and in response,selectively gate the dynamic clock signal based on the fixed clockgating control value to generate a fixed clock signal having a fixedclock frequency, wherein the fixed clock signal frequency remainsconstant regardless of the performance indicator value.
 8. The adaptivefrequency scaling circuitry of claim 7, wherein the scaling circuitrycomprises: a plurality of lookup tables that input a respectiveplurality of performance indicator values and output a respectiveplurality of dynamic clock gating control values and a respectiveplurality of fixed clock gating control values; and selection circuitryconfigured to: select one of the plurality of dynamic clock gatingcontrol values; select one of the plurality of fixed clock gatingcontrol values, such that the selected fixed clock gating control value,when used to gate the dynamic clock signal, will generate a fixed clocksignal having the fixed clock signal frequency; and provide the selecteddynamic clock gating control value and the selected fixed clock gatingcontrol value to the clock gating circuitry.
 9. The adaptive frequencyscaling circuitry of claim 1, wherein the scaling control circuitryfurther comprises trigger circuitry configured to cause the scalingcontrol circuitry to determine a subsequent desired dynamic clockfrequency for the data processing system on every xth cycle of the inputclock signal, where x is a predetermined integer.
 10. A method,comprising: receiving a performance indicator value indicative of anoperating parameter of a data processing system; selecting a dynamicclock gating control value based at least on the performance indicatorvalue, wherein selecting a dynamic clock gating control value comprisesinputting the performance indicator value to a lookup table andselecting an output of the lookup table as the clock gating controlvalue; and gating an input clock signal based at least on the dynamicclock gating control value to generate a dynamic clock signal.
 11. Themethod of claim 10, further comprising: selecting a fixed clock gatingcontrol value based on the dynamic clock gating control value and afixed clock frequency; and gating the dynamic clock signal based atleast on the fixed clock gating control value to generate a fixed clocksignal having the fixed clock frequency.
 12. The method of claim 10,wherein gating the input clock signal to generate the dynamic clocksignal comprises, for each cycle of the input clock signal: inputtingM+1 bits corresponding to the dynamic clock gating control value to anaccumulator having M+1 bits; inputting M bits corresponding to bitsM−1:0 of the accumulator at a prior input clock cycle to theaccumulator; and passing an input clock signal pulse in response to bitM of the accumulator being
 1. 13. The method of claim 12, furthercomprising determining the dynamic clock gating control value as aproduct of a desired dynamic clock signal frequency and 2M divided by aninput clock frequency of the input clock signal.
 14. The method of claim10, further comprising: receiving a performance indicator valueindicative of a plurality of operating parameters of a data processingsystem; determining a plurality of dynamic clock gating control values,wherein each of the determined dynamic clock gating control values inthe plurality of dynamic clock gating control values is based adifferent one of the plurality performance indicator values; selecting amaximum dynamic clock gating control value from amongst the determineddynamic clock gating control values; and gating an input clock signalbased at least on the maximum dynamic clock gating control value togenerate the dynamic clock signal.
 15. The method of claim 10 whereinthe performance indicator value is indicative of one or more of ahighest interface rate amongst active links between the data processingsystem and external devices, a highest interface rate amongst activelinks between the data processing system and the external devices, and aqueue length in a shared packet buffer in the data processing system.16. A method, comprising: until all active interfaces have beenanalyzed: identifying an active interface between a data processingsystem and an external device; increasing a total rate value by a linkrate of the active interface; and replacing a highest rate value withthe link rate when the link rate is higher than the highest rate value;selecting a first dynamic clock gating control value based on the totalrate value; selecting a second dynamic clock gating control value basedon the highest rate value; selecting a third dynamic clock gatingcontrol value based on a queue length value; and providing, to a clockgating circuitry, a maximum of the first dynamic clock gating controlvalue, the second dynamic clock gating control value, and the thirddynamic clock gating control value as a dynamic clock gating controlvalue, wherein the clock gating circuitry generates a dynamic clocksignal from an input clock signal based at least on the maximum dynamicclock gating control value.
 17. The method of claim 16, furthercomprising: selecting a first fixed clock gating control value based onthe total rate value; selecting a second fixed clock gating controlvalue based on the highest rate value; selecting a third fixed clockgating control value based on a queue length value; and providing, to asecond clock gating circuitry, a minimum of the first fixed clock gatingcontrol value, the second fixed clock gating control value, and thethird fixed clock gating control value as a fixed clock gating controlvalue, wherein a second clock gating circuitry generates a fixed clocksignal from the dynamic clock signal based at least on the minimum fixedclock gating control value.